Distinctive features:  
Ball-like structures, often enclosing shell fragment or other nuclei. Composed of sandstone or clay cemented by calcite or silica, the internal shrinkage cavities, usually filled with calcite, may be seen when the nodule is cut or broken.

Colour: 
Variable: grey to buff to dark brown with white-yellow calcite filling the interior, radiating cracks and cavities.

Texture and granularity: 
Usually fine-grained.

Composition: 
Variable, depending on origin. Sand, silt or clay together with calcite.

Field associations: 
Fine-grained or clay sediments.

 

Worldwide.

 

Ornamental when cut or polished.